This invention relates to an adjustless V-belt and a method of manufacturing the same, and more particularly to a power transmitting adjustless V-belt which automatically absorbs and adjusts its elongation resulting during operation, to thereby maintain the tension constant.
Wrapping connector driving belts such as flat belts, V-belts, and poly-V-belts serve, in general, to transmit power through the frictional force thereof. Accordinly, the belt needs a tension predetermined according to the driving conditions. If the belt is elongated and the tension is decreased during the run, then the force of the belt gripping the pulley is decreased. As a result, the belt slips. If the belt slips in this manner, then heat is generated in the belt, and the belt is therefore further elongated while the degree of slip of the belt is also further increased. Finally, the belt may be broken earlier than is normal service life by the heat generated therein. Accordingly, in order to improve the durability of the belt, it is necessary to provide a belt which is elongated to a negligable extent and can maintain a tension higher than a threshold value at which slip is caused.
Recently, a technical concept has been studied with interest in which a rope having a great thermal contraction stress, such as a synthetic fiber rope made of, for instance, polyester fibers, is used as the tensile member of a belt, so that, when heat is generated in the belt to elongate the latter, the tensile member reacts quickly with the generation of heat in the belt to contract the belt thereby to suppress the elongation of the belt. During a series of belt manufacturing processes, the thermal elongation treatment of the rope tensile member is extensively carried out in order to reduce the elongation of the rope tensile member before the belt molding process. However, as the degree of thermal elongation treatment for the synthetic fiber rope is increased, the thermal contraction stress is increased during vulcanization. Accordingly, when the synthetic fiber rope spirally wound on a cylindrical drum or a metal mold through a rubber layer not vulcanized yet is subjected to vulcanization, then the rope tensile member is contracted by the contraction stress. As a result, it is dropped in the rubber layer, and the contraction stress is reduced. Thus, the resultant belt is high in elongation. At worst, the rope tensile member in the rubber layer is disturbed, and it is difficult to maintain the pitch line of the rope tensile member regular.
The above-described drawbacks accompanying a conventional method of manufacturing a rubber V-belt or a V-belt with cogs, and secondary difficulties which are involved in counter-measures effected to eliminate the drawbacks will be described with reference to FIGS. 1 through 5.
As shown in FIG. 1 a few plys of rubberized canvas 24 are wound around a cylindrical metal method mold 21 or a metal mold (not shown) on the outer wall of which protrusions are formed. A compressive rubber sheet 22 and an adhesion rubber 23a, which are not vulcanized yet, are laminated on the rubberized canvas layer 24. Then, a rope tensile member 26 made of polyester fibers having a large thermal contraction stress is wound spirally on the adhesion rubber sheet 23a. Thereafter, an adhesion rubber 23b not yet vulcanized of several plys of rubberized canvas 25 are wound on the rope tensile member 26 in succession, to form an assembly. Then, the assembly is externally pressurized and heated to obtain a molded belt blank. Thereafter, the molded belt blank is cut into a plurality of rings to provide V-belts.
In this method of manufacturing V-belts, the rope tensile member 26 is embedded in the adhesion rubber layers 23b and 23a as the latter flow under the application of heat and pressure. However, the amount of rubber flowing between the parts of the rope tensile member spirally wound is very small, and the degree of friction obtained by the flow of rubber is therefore small. Thus, it is difficult to activate the surface of the rope tensile member 26. Also, various blending chemicals and softeners are mixed in the adhesion rubber layers 23b and 23a and are not yet vulcanized. Therefore, the surfaces of the adhesion rubber layers 23a and 23b are unsatisfactory in terms of adhesion property. Thus, in combination with the rope tensile member 26 having the inert surface, it becomes difficult to bond the rope tensile member to the adhesion rubber layers 23a and 23b.
Furthermore, since the rope tensile member 26 having the thermal contraction characteristic is wound on the flexible rubber layer not yet vulcanized, the rope tensile member is contracted during vulcanization. As a result, it is dropped as indicated by the arrows (FIG. 1) in the adhesion rubber layer 23a and the compressive rubber layer 22 below the rope tensile member. Thus, as shown in FIG. 2, the arrangement of the parts of the rope tensile member 26, i.e., the pitch line thereof becomes irregular. Accordingly, tension is non-uniformly applied to the parts of the rope tensile member 26, whereby the belt may fail prematurely.
In order to eliminate the above-described difficulty where the tensile member is dropped in the rubber layer by thermal contraction, a method may be employed in which, as shown in FIG. 3, a reinforcing canvas layer 28 is provided below the rope tensile member 26 to prevent the rope tensile member from dropping in the rubber layer. In this case, however, the rope tensile member 26 embedded in the adhesion rubber layer 23 is dropped in the lower part of the adhesion rubber layer 23, to be brought into contact with the reinforcing canvas 28. Therefore, the reinforcing canvas may separate the belt into layers.
FIG. 4 shows a reversal molding method. An upper rubberized canvas 25, an adhesion rubber layer 23, a rope tensile member 26, a compressive rubber layer 22 and a lower rubberized canvas 24 are wound on a metal mold 21 in succession to form an assembly. The assembly is pressurized and heated to provide a molded belt blank, and the molded belt blank is cut into a plurality of rings. These are turned inside out to provide the composite belt. In this conventional method also, it is difficult to prevent the rope tensile member from dropping into the rubber layer; that is, the rope tensile member 26 is caused to drop into the adhesion rubber layer 23 as indicated by the arrows. As a result, the rope tensile member 26 is brought into contact with the upper rubberized canvas layer 25 as shown in FIG. 5. Thus, in this case also, the above-described trouble may be caused with respect to the surface where the tensile member is provided.
As is apparent from the above description, in the above-described various methods, no rubber layer is provided between the tensile member and the reinforcing canvas or the upper rubberized canvas layer, i.e., the tensile member is in direction contact with the canvas, and therefore the adhesion property of the rope tensile member is lowered. Thus, the tensile member is liable to peel off during the run of the belt. Thus, the conventional methods described above are still disadvantageous in many respects.